1. Field of the Invention
The present invention relates to a heater module for heating an optical waveguide device so as to regulate the temperature of the optical waveguide device, and an optical waveguide device equipped with the same.
2. Related Background Art
If an optical waveguide module has a large temperature distribution within an optical waveguide device, the size of the optical waveguide will vary due to differences in thermal expansion of its substrate depending on locations, thereby damaging its wavelength selectivity and switching characteristics. Therefore, an uniformity in temperature is required within the optical waveguide device.
As a device for regulating the temperature of optical waveguide devices, thermoelectric cooling module and heaters have conventionally been utilized. Since it is necessary for an optical waveguide module to draw thereinto an optical fiber used for transmitting optical signals with respect to external devices, hermetic sealing is difficult at the drawing portion. Therefore, it is impossible for thermoelectric cooling module to secure their reliability, whereby heaters are often used as a temperature-regulating device. In a heater, a heat-generating circuit (resistance) adapted to generate heat when energized is provided within an insulating layer, whereby the heat from the heat-generating circuit is transmitted to the optical waveguide device by way of the insulating layer.
Conventionally, ceramics heaters made of alumina having a relatively low thermal conductivity (thermal conductivity of 20 W/mK) and the like have often been used. However, tendencies toward larger capacities and higher-speed communications have nowadays become remarkable, in particular, in the field of optical communications. Recently, along with the shift to D-WDM (Dense Wavelength Division Multiplexing), optical waveguide devices having large areas have come into use. Further, there has been an increasing demand for multiplexing a greater number of signals than those conventionally multiplexed for a certain frequency width, thereby enhancing the demand for uniformity in temperature. Hence, it is desired that the uniformity in temperature within the optical waveguide device be further improved (to become xc2x10.5xc2x0 C. or less).
In order to satisfy such a demand for uniformity in temperature of the optical waveguide device, two methods have currently been under consideration. The first method is one using a heat spreader employing a Cu alloy or the like having a favorable thermal conductivity. It is a method in which the heat generated by an alumina heater is once uniformly dispersed by the heat spreader and then is transmitted to the optical waveguide device, so as to improve the uniformity in temperature. The second method is one in which the heater itself is formed from AlN or the like having a thermal conductivity (thermal conductivity of 170 W/mK) which is about 10 times that of conventionally used alumina, so that the heat generated by the heater is uniformly dispersed by the heater itself and then is transmitted to the optical waveguide device, whereby the uniformity in temperature is improved. When these methods are employed, the temperature distribution of the optical waveguide device can be made xc2x10.5xc2x0 C. or less.
However, demands for D-WDM have recently been becoming severer in a drastic manner, whereby further multiplexing is desired. As a consequence, a temperature uniformity higher than that conventionally achieved is required for optical waveguide devices. Further, photonic networks making full use of optical switching and the like without using electric devices at all have been under consideration. For realizing them, devices using new materials such as LiNbO3 and resin waveguides, which are different from conventional quartz and silica, have been under consideration as optical waveguide devices. For these devices, a temperature uniformity severer than that conventionally demanded is required, and there is a case where a temperature uniformity of xc2x10.1xc2x0 C. or less is required for an optical waveguide device.
In order to overcome such problems, as shown in FIG. 7, an attempt to realize a temperature uniformity of xc2x10.1xc2x0 C. or less was carried out by utilizing the fact that the temperature uniformity of an optical waveguide device 71 improves when the thickness of a ceramics heater 73 or the thickness of a heat spreader 72 is enhanced. In this case, though the temperature uniformity in the optical waveguide device 71 was maintained in its surface bonded to the ceramics heater 73 or heat spreader 72, the surface opposite from the one bonded to the ceramics heater 73 or heat spreader 72 was exposed to an ambient temperature, whereby the optical waveguide device 71 was cooled, thus failing to realize a temperature uniformity of xc2x10.1xc2x0 C. or less.
In order to prevent the upper part of the optical waveguide device 71 from being cooled, there maybe considered a method in which the optical waveguide device 71 is heated by a heater from both upper and lower faces of the optical waveguide device 71, or a method in which the heater for heating is not constituted by ceramics but by a silicone 74 or polyimide heater, which can be bent freely as shown in FIG. 8, and the heater is processed into a tubular form having a center part at which the optical waveguide device 71 is installed.
However, the above-mentioned methods heat not only the optical waveguide device 71 but also the whole optical module, thereby being problematic in that the power consumption increases to about two times or more that in the case where heating is effected from only the lower face of the optical waveguide device 71. Also, they are problematic in that the optical waveguide module inevitably increases its thickness. While an optical waveguide module is required to have a thickness of about 10 mm, which is typical as a module other than the optical waveguide module, the thickness of the optical waveguide module becomes about 20 to 30 mm in the above-mentioned methods. Therefore, in an apparatus equipped with the optical waveguide module, design rules for designing an apparatus constituted by other devices alone are not applicable, so that a special design is necessary, whereby not only the efficiency in designing and the cost of design, but also the cost of the whole apparatus increases.
Therefore, it is an object of the present invention to provide a heater module which can improve the temperature uniformity in an optical waveguide while keeping the power consumption and the thickness of the optical waveguide module by overcoming the problems mentioned above, and an optical waveguide module equipped therewith.
The heater module in accordance with the present invention is a heater module for heating an optical waveguide device so as to regulate a temperature of the optical waveguide device, the heater module comprising a heat-generating circuit adapted to generate heat when energized; and a heat-transmitting section disposed on an upper face of the heat-generating circuit and formed with a recessed groove portion for mounting the optical waveguide device.
In the present invention, the heat-transmitting section for heating an optical waveguide device is formed with a recessed groove portion, and the optical waveguide device is mounted in this recessed groove portion. The inventors have found that such a configuration makes it possible to heat the optical waveguide device not only from its bottom face but also from its side faces by way of edge parts constituting the recessed groove portion, whereby the temperature uniformity can be enhanced. Since the heat is transmitted from the edge parts of the recessed groove portion formed in the integral heat-transmitting section in the configuration of the present invention, it is not necessary to provide respective heaters 75 for generating heat at the bottom and side faces as shown in FIG. 9. Also, since the optical waveguide device can be mounted so as to be inserted into the recessed groove portion formed in the heat-transmitting section, no heat-transmitting section for heating the upper face of the optical waveguide device is necessary, whereby a simple configuration can realize a heater module capable of enhancing the temperature uniformity. As a consequence, the thickness of the optical waveguide module using the optical waveguide device can be kept on a par with that in the case where the optical waveguide device is simply mounted on the heat-transmitting section.
In the heater module, the heat-transmitting section may be constituted by AlN ceramics.
When the heat-transmitting section is thus constituted by AlN ceramics having a high thermal conductivity, the temperature uniformity of the heated optical waveguide device can further be enhanced.
Preferably, in the heater module, an insulating layer is disposed between the heating circuit and the heat-transmitting section.
The optical waveguide module in accordance with the present invention comprises the above-mentioned heater module, an optical waveguide device mounted in a recessed groove portion formed in the heat-transmitting section, and a housing accommodating the heater module and the optical waveguide device.
When an optical waveguide module for heating an optical waveguide device is constituted by using the above-mentioned heater module as such, the temperature uniformity of the optical waveguide device can be enhanced, and the optical waveguide module can be realized by a simple configuration, whereby the thickness of the optical waveguide module can be kept on a par with that in the case where the optical waveguide device is simply mounted on the heat-transmitting section.
Preferably, a gaseous medium is interposed in a space defined between an edge part of the recessed groove portion and the optical waveguide device, and the upper face of the edge part constituting the recessed groove portion is higher than the upper face of the optical waveguide device mounted on the bottom face of the recessed groove portion, or has a level difference not greater than 0.1 mm with respect to the upper face of the optical waveguide device or not greater than {fraction (1/10)} of the height of the optical waveguide device.
The edge part of the recessed groove portion acts to transmit the heat, which is transmitted to the heat-transmitting section, to the optical waveguide device. The heat from the edge part is transmitted by way of the gaseous medium interposed between the optical waveguide device and the edge part. When the upper face of the edge part is lower than the upper face of the optical waveguide device, the heat is transmitted to the optical waveguide device up to the height of the upper face of the edge part but not to its portion higher than the edge part. In this case, the upper face of the optical waveguide device is cooled by the ambient temperature. As a result of simulations of the relationship between the height of the edge part and the temperature uniformity, it has been found that, in the case where the upper face of the edge part is higher than the upper face of the optical waveguide device or where the upper face of the optical waveguide device is higher than the edge part, a desirable temperature uniformity (xc2x10.1xc2x0 C. or less) can be realized when their difference is not greater than 0.1 mm or not greater than {fraction (1/10)} of the height of the optical waveguide device.
Preferably, a gaseous medium is interposed in a space defined between an edge part of the recessed groove portion and the optical waveguide device, and the space defined between the edge part of the recessed groove portion and the optical waveguide device has a width of at least 0.02 mm but not greater than 1.0 mm.
If the width of the space between the edge part and the heat-transmitting section is shorter than 0.02 mm, a portion where the heat-transmitting section and the optical waveguide device partly come into contact with each other will occur due to problems in the processing accuracy of the heat-transmitting section, whereby the temperature uniformity of the optical waveguide device cannot be secured. If the width of the space between the edge part and the heat-transmitting section is greater than 1.0 mm, heat cannot efficiently be transmitted to side faces of the optical waveguide device when convection occurs within the optical waveguide module due to partial temperature differences and the like, whereby the temperature uniformity cannot be secured. Therefore, it is preferred that the width of the space between the edge part and the heat-transmitting section be at least 0.02 mm but not greater than 1.0 mm. Further, according to the structure of the optical waveguide module, it is desirable that the width of the space be 0.5 mm or less in order to keep the convection from influencing the space.
The optical waveguide module may further comprise a resin interposed in a space defined between the edge part and the optical waveguide device.
When a resin is interposed in a space defined between the edge part and the optical waveguide device as such, the resin can transmit heat from the heat-transmitting section to the optical waveguide device.
In the optical waveguide module, the resin may be composed of a grease-like material.
When a grease-like resin is used as such, no thermal stress acts on side faces of the optical waveguide device. Therefore, even when an optical waveguide susceptible to stress is used, the danger of damaging the optical waveguide device can be lowered.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.